Chemical and isotopic characteristics of the Didwana-Rajod (H5) chondrite

The mineralogical and chemical characteristics of the Didwana-Rajod chondrite are described. The mean mineral composition is found to be olivine (Fo(83.2)) and pyroxene (En(83.5)Wo(0.7)Fs(15.8)), and feldspar is mainly oligoclase. Oxygen isotopic analysis shows delta (18)O = +3.8 parts per thousand and delta (17)O = +2.59 parts per thousand. The nitrogen content of Didwana-Rajod is similar to2 ppm with delta (15)N approximate to3.4 parts per thousand. Based on microscopic, chemical, isotopic and electron probe microanalysis, the meteorite is classified as an H5 chondrite. Cosmogenic tracks, radionuclides and the isotopic composition of rare gases were also measured in this meteorite. The track density in olivines varies in a narrow range with an average value of (6.5 +/- 0.5) x 10(5)/cm(2) for four spot samples taken at the four corners of the stone. The cosmic-ray exposure age based on neon and argon is 9.8 Ma. (22)Na/(26)Al approximate to 0.94 is lower than the solar-cycle average value of similar to1.5 and is consistent with irradiation of the meteoroid to lower galactic cosmic-ray fluxes as expected at the solar maximum. The track density, rare gas isotopic ratios, (60)Co activity and other radionuclide data are consistent with a preatmospheric radius of similar to 15 cm, corresponding to a mass of similar to 50 kg. The cosmogenic properties are consistent with a simple exposure history in interplanetary space.